Today, a variety of different hosts including plants, algae, fungi, stramenopiles and yeast are being investigated as means for commercial PUFA production. Genetic engineering has demonstrated that the natural abilities of some hosts (even those natively limited to linoleic acid (LA; 18:2 ω-6) and α-linolenic acid (ALA; 18:3 ω-3) fatty acid production) can be substantially altered to result in high-level production of various long-chain ω-3/ω-6 PUFAs. Whether this is the result of natural abilities or recombinant technology, production of arachidonic acid (ARA; 20:4 ω-6), eicosapentaenoic acid (EPA; 20:5 ω-3) and docosahexaenoic acid (DHA; 22:6 ω-3) may require expression of a Δ9 elongase.
Most Δ9 elongase enzymes identified so far have the ability to convert both LA to eicosadienoic acid (EDA; 20:2 ω-6) and ALA to eicosatrienoic acid (ETrA; 20:3 ω-3) (wherein dihomo-γ-linolenic acid (DGLA; 20:3 ω-6) and eicosatetraenoic acid (ETA; 20:4 ω-3) are subsequently synthesized from EDA and ETrA, respectively, following reaction with a Δ8 desaturase; ARA and EPA are subsequently synthesized from DGLA and ETA, respectively, following reaction with a Δ5 desaturase; and, DHA synthesis requires subsequent expression of an additional C20/22 elongase and a Δ4 desaturase).
In spite of the need for new methods for the production of ARA, EPA and DHA, few Δ9 elongase enzymes have been identified. A Δ9 elongase from Isochrysis galbana is publicly available (described in GenBank Accession No. AAL37626, as well as PCT Publications No. WO 02/077213, No. WO 2005/083093, No. WO 2005/012316 and No. WO 2004/057001). PCT Publications No. WO 2007/061845 and No. WO 2007/061742 (Applicants' Assignee's co-pending applications), disclose Δ9 elongases from Euglena gracilis and Eutreptiella sp. CCMP389, as well as Δ9 elongase motifs.
Thus, there is need for the identification and isolation of additional genes encoding Δ9 elongases that will be suitable for heterologous expression in a variety of host organisms for use in the production of ω-3/ω-6 fatty acids.
Applicants have solved the stated problem by isolating genes encoding Δ9 fatty acid elongases from Euglena anabaena. 